Current high stressed aircraft/aerospace, military, automotive, and oil/gas members are made of expensive high strength, high toughness steels. They have an ultimate tensile strength of about 250 to 300 ksi, a yield strength of about 200 to 250 ksi, a an Charpy v-notch impact toughness energy of about 18 to 36 ft-lbs, and a fracture toughness (Klc) of about 50 to 110 ksi√in. As used herein a high-strength, high toughness steel has or exceeds these physical properties.
AerMet 100 and Marage 250 are examples of high cost high strength, high toughness alloy steels that are used in aircraft/aerospace. AerMet 100, the most costly, has by weight 13.4% of cobalt (Co), 1.2% of molybdenum (Mo), and 11.1% of nickel (Ni). Its high cost is due to large amounts of expensive alloying elements and high energy consuming processes, such as vacuum arc remelting (VAR) and electroslag remelting (ESR).
300M and AISI 4340 steels are examples of high strength, moderate impact toughness steels that are used for aircraft/aerospace members. They have by weight 1.65 to 2.0% of Ni and 0.2 to 0.65% of Mo.
U.S. Pat. No. 7,067,019 is an example of a high strength steel without Co and Mo and with content of Ni varying from about 1.0 to about 8.0%. Its cost is comparable to high strength steels, such as 300M, and 4340, but its toughness is higher.
U.S. Pat. No. 6,426,038 is an example of a low cost, high strength, moderate toughness steel in which the elements cobalt, molybdenum, and nickel are eliminated.